The present invention relates to a method for treating powdered coal in an installation for injecting solid fuels, comprising a powdered coal storage bunker, at least one lock connected to the circuit for pneumatically transporting the coal, at least one filtering screen connected between each lock and the bunker, a pressurized inert-gas source for pressurizing each lock and forming the pneumatically propelled flow of the coal and a circuit for pressure-equalizing and depressurizing each lock through a filter. The invention also relates to a device for the implementation of this method.
An installation of this general kind is described in U.S. Pat. No. 4,702,288, which is incorporated herein by reference. The coal used in this kind of installation is generally delivered loose and is broken up, ground and dried in place. The grinding is carried out, for example, in a vertical grinding mill in which the coal is crushed on a rotary milling track by milling rollers. The coal powder is entrained by drying gases into a separator, from which it is dumped into the storage bunker of the installation for injection into a furnace.
The relative humidity poses a certain number of problems in the storage bunker. In fact, because of the drying of the coal, the drying gas accumulates a large quantity of water vapor which, as the bunker cools, is condensed above the mass and is responsible for an agglomeration and for an encrustation of the coal powder.
Moreover, because of heat exchanges and thermal equilibria within the mass of the coal powder, the coal powder "transpires", which also creates a gaseous environment rich in water vapor within the interstices of the mass of coal. This water vapor within the mass of coal is entrained out of the bunker into the filter screen where, by condensing, it creates the risk of clogging up the screening elements.